Request for assistance: mapping charsets

Matter at hand: gh-ost's support for multiple charsets.

gh-ost works well out-of-the-box with utf8 and utf8mb4.

However for other character sets it needs to be told, explicitly, how to convert strings. For example, the latin1 character set is supported, and is converted via golang's charmap.Windows1252, see: https://github.com/github/gh-ost/blob/master/go/sql/encoding.go#L20

If anyone is willing to assist in mapping other MySQL charsets to golang Encoders, we're very grateful. Please PR the https://github.com/github/gh-ost/blob/master/go/sql/encoding.go file with additional charsets.